I've been using QGIS 2.14 pretty successfully for about two years. I do also have Arc but tend to use Q more primarily because it did run considerably faster. I then installed QGIS 3 as I noticed it had some really useful functions such as the 'multi edit tool' for the attribute table. However the difference in speed between the two versions is drastic, particularly when working with 'layer properties' or the print composer. More often than not when I open the properties menu my computer freezes and I can go and make a coffee before it's even opened and that's before I've tried to make any changes. Even moving the cursor around at that stage can lead to a 'not responding message'.
As I've not seen any other comments to this effect I can only assume I'm missing something. Perhaps a setting or something. As far as I'm aware I'm not using the program any differently than I was the previous version, but it's currently making a program that transformed the way I work into something that is almost unusable.